A surface modification method for graphite plate

Abstract

The present invention discloses a surface modification method for a graphite plate, which relates to the field of fuel cell technology and comprises the following steps: S1, designing a printing pattern of a screen printing plate according to the flow channel structure of the finished graphite plate so that the mesh of the screen printing plate is aligned with the flow channel; S2, applying a hydrophobic agent to the flow channel by screen printing; S3, curing the finished graphite plate coated with the hydrophobic agent so that a hydrophobic layer is formed in the flow channel. The present invention adopts a screen printing process to apply a hydrophobic agent to the flow channel and cures it to form a first hydrophobic layer and a second hydrophobic layer with different heights. The overall process is simple, easy to operate, and can be promoted and used on a large scale. The preparation method provided by the present invention is to directly modify the surface of the finished graphite plate, so there is no problem of the hydrophobic layer being destroyed by the impregnation or resin curing process, so that the hydrophobic layer structure of the graphite plate is more reliable, effectively overcoming the problems existing in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a surface modification method for a graphite plate. Background Art

[0002] A fuel cell is a power generation device that generates electricity through an electrochemical reaction between hydrogen and oxygen (from the air). Proton exchange membrane fuel cells are considered a promising new energy technology due to their high conversion efficiency, zero pollution, and strong environmental adaptability.

[0003] Bipolar plates are the core components of fuel cell stacks, providing mechanical support, separating oxidants and reductants, and conducting heat and electricity. As fuel cell heavy-duty trucks continue to increase the power required by fuel cell stacks, the active area of ​​the bipolar plates is increasing, placing higher demands on their mass transfer and drainage capabilities.

[0004] Currently, there are two common processes for manufacturing graphite bipolar plates on the market: machining (CNC machining) and compression molding. Both the high-temperature graphite raw materials used in machining and the flexible graphite plates used in compression molding exhibit a certain degree of hydrophilicity due to the graphite's inherent surface energy and porosity. Therefore, relying solely on air purging cannot completely remove liquid water from the surface of the graphite bipolar plates. Instead, it increases flow resistance within the pipeline and parasitic power consumption of the air compressor. Furthermore, any liquid water that is not removed during shutdown purge can freeze into ice at low temperatures, affecting cold start performance.

[0005] In order to solve this problem, the Chinese patent application number 202211485705.8 discloses a surface-modified graphite plate and its preparation method and application. The scheme uses a hydrophobic agent to form a hydrophobic layer on the bottom surface of the flow channel groove of the gas flow field, thereby effectively improving the drainage capacity of the bottom of the flow field. However, the preparation of the hydrophobic layer in this scheme is completed in the flow channel molding process of the semi-finished graphite plate. After that, the semi-finished graphite plate needs to be impregnated, cleaned, cured and dried to obtain the finished molded graphite plate. During the impregnation process, the semi-finished graphite plate needs to be placed in a pressurized environment so that the resin solution is fully impregnated into the interior of the plate. During the curing process, it is also necessary to ensure that the deep resin inside the plate is fully cross-linked and cured, so as to ensure the mechanical strength of the finished graphite plate. Therefore, the impregnation and curing processes will damage the prepared hydrophobic layer, resulting in the failure of the hydrophobic properties of the finished graphite plate. Summary of the Invention

[0006] The present invention provides a surface modification method for a graphite plate, the main purpose of which is to solve the problem in the prior art that the hydrophobic performance of the graphite plate fails due to an unreasonable preparation method of the hydrophobic layer.

[0007] The present invention adopts the following technical solutions:

[0008] A surface modification method for a graphite plate comprises the following steps:

[0009] S1. Design the printing pattern of the screen printing plate according to the flow channel structure of the finished graphite plate so that the mesh of the screen printing plate is aligned with the flow channel;

[0010] S2. Applying a hydrophobic agent to the flow channel by screen printing;

[0011] S3. Curing the finished graphite plate coated with the hydrophobic agent to form a hydrophobic layer in the flow channel.

[0012] Furthermore, in step S3, the hydrophobic layer includes a plurality of first hydrophobic layers and second hydrophobic layers that are alternately arranged, and the height of the second hydrophobic layer is greater than the height of the first hydrophobic layer and less than the height of the flow channel groove.

[0013] Furthermore, in step S1, the same flow channel is divided into a plurality of first coating areas and second coating areas which are alternately arranged, and the aperture of the silk-screen mesh corresponding to the first coating area is smaller than the aperture of the silk-screen mesh corresponding to the second coating area; in step S2, a hydrophobic agent is coated on the first coating area and the second coating area of ​​the flow channel through a silk-screen screen, so that the hydrophobic agent in the first coating area is less than the hydrophobic agent in the second coating area; in step S3, the finished graphite plate coated with the hydrophobic agent is cured, so that the first hydrophobic layer and the second hydrophobic layer are formed in the first coating area and the second coating area, respectively.

[0014] Furthermore, in step S1, the same flow channel is divided into a number of first coating areas and second coating areas that are alternately arranged, and a first silk screen screen and a second silk screen screen are made, the mesh holes of the first silk screen screen are aligned with the first coating area and the second coating area, and the mesh holes of the second silk screen screen are aligned with the second coating area; in step S2, the hydrophobic agent is first evenly coated on the first coating area and the second coating area of ​​the flow channel through the first silk screen screen, and then the hydrophobic agent is coated on the second coating area through the second silk screen screen; in step S3, the finished graphite plate coated with the hydrophobic agent is cured so that the first hydrophobic layer and the second hydrophobic layer are formed in the first coating area and the second coating area, respectively.

[0015] Furthermore, the second hydrophobic layers in two adjacent flow channel grooves are arranged in a staggered manner.

[0016] Furthermore, the height difference between the second hydrophobic layer and the first hydrophobic layer is 0.2-0.3 mm.

[0017] Furthermore, in step S2, the screen printing scraper pressure is 5-25 kPa, and the scraper speed is 1-20 cm / min.

[0018] Furthermore, in step S3, a curing furnace is used to cure the finished graphite plate coated with the hydrophobic agent at a curing temperature of 100-200°C.

[0019] Furthermore, in step S2, the hydrophobic agent is selected from at least one of polytetrafluoroethylene, polyvinylidene, epoxy resin, polyphenylene sulfide and polyimide, and the viscosity of the hydrophobic agent is 5-30 cP.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention uses a screen printing process to apply a hydrophobic agent to the flow channel and solidify it to form a first hydrophobic layer and a second hydrophobic layer of different heights. The overall process is simple, easy to operate, and can be promoted and used on a large scale. Compared with the existing technology, the preparation method provided by the present invention directly modifies the surface of the finished graphite plate. Therefore, there is no problem of damage to the hydrophobic layer by impregnation or resin curing process, making the hydrophobic layer structure of the graphite plate more reliable, effectively overcoming the problems existing in the existing technology.

[0022] 2. The present invention effectively improves drainage performance within the flow channel by providing a hydrophobic layer, allowing liquid water in the graphite plate flow channel to be promptly purged, preventing residual liquid water. This reduces the purge metering ratio and reduces parasitic power consumption of the air compressor. Due to the height difference between the first and second hydrophobic layers, the flow channel bottom exhibits an undulating pattern, which blocks and guides the reactant gases, facilitating their diffusion toward the catalyst layer. This effectively improves mass transfer and reduces concentration polarization at high current densities. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the structure of the graphite plate in the present invention.

[0024] Figure 2 Schematic cross-sectional view of the graphite plate of the present invention.

[0025] Figure 3 The figure is a flow chart of the method for modifying the graphite plate of the present invention.

[0026] Figure 4 This is a flow chart of the preparation method of the first embodiment of the present invention.

[0027] Figure 5 This is a flow chart of the preparation method of the second embodiment of the present invention.

[0028] In the figure: 1-plate body; 11-flow channel; 2-first hydrophobic layer; 21-first inclined platform; 3-second hydrophobic layer; 31-second inclined platform. DETAILED DESCRIPTION

[0029] The specific embodiments of the present invention are described below with reference to the accompanying drawings. In order to fully understand the present invention, many details are described below, but for those skilled in the art, the present invention can be implemented without these details.

[0030] Reference Figure 1 and Figure 2 The present invention discloses a graphite electrode, comprising an electrode body 1 and a hydrophobic layer, wherein the hydrophobic layer comprises a first hydrophobic layer 2 and a second hydrophobic layer 3. The surface of the electrode body 1 has a plurality of flow channels 11, and a plurality of first hydrophobic layers 2 and second hydrophobic layers 3 are provided in the same flow channel 11 at intervals. The height of the second hydrophobic layer 3 is greater than the height of the first hydrophobic layer 2 and less than the height of the flow channel 11. The present invention effectively improves the drainage performance in the flow channel 11 by providing the first hydrophobic layer 2 and the second hydrophobic layer 3, so that the liquid water in the flow channel of the graphite electrode can be purged in time, avoiding liquid water residue, thereby reducing the purge metering ratio and reducing the parasitic power consumption of the air compressor. Due to the height difference between the first hydrophobic layer 2 and the second hydrophobic layer 3, the bottom of the flow channel 11 presents an undulating shape, which can block and guide the reaction gas, facilitate the diffusion of the reaction gas toward the catalyst layer, effectively improve the mass transfer effect, and reduce concentration polarization under high current density.

[0031] Reference Figure 1 The second hydrophobic layers 3 within two adjacent flow channels 11 are staggered. This design ensures effective diffusion of the reactant gases within each flow channel 11 to the catalyst layer while maintaining drainage performance. Because the first and second hydrophobic layers 2 and 3 are applied only to the bottoms of the flow channels 11 and not to the ridges at the tops of the channels 11, they do not affect the ridges in contact with the membrane electrode, thereby maintaining overall conductivity.

[0032] Reference Figure 1 and Figure 2 The ends of the first hydrophobic layer 2, located at both ends of the flow channel 11, are provided with first ramps 21 for easy air intake and drainage. A second ramp 31 is also provided on the top of the second hydrophobic layer 3 for easy air intake and drainage. The design of the first ramp 21 and the second ramp 31 serves as a guide, facilitating the timely discharge of liquid water from the flow channel 11 and the diffusion of the reactant gas into the catalyst layer.

[0033] Reference Figure 1 and Figure 2In order to ensure that the second hydrophobic layer 3 can block and guide the reaction gas, the height difference between the second hydrophobic layer 3 and the first hydrophobic layer 2 should be 0.2-0.3mm during design. Since the air inlet pressure has a continuous purge effect on the flow channel groove, and the arrangement of the first hydrophobic layer 2 and the second hydrophobic layer 3 is conducive to drainage, the second hydrophobic layer will not block the liquid water and can ensure that the liquid water is quickly purged. Since the second hydrophobic layer 3 is arranged above the first hydrophobic layer 2 at intervals, it will not occupy too much space in the flow channel groove 11, will not affect the drainage volume of the flow channel groove 11, and will not affect the conductivity of the electrode body 1. As a preferred embodiment, in this embodiment, the total height H1 of the electrode body 1 is 1.2mm, the height H2 of the flow channel groove 11 is 0.7mm, the height H3 of the first hydrophobic layer 2 is 0.2mm, and the height H4 of the second hydrophobic layer 3 is 0.5mm. Therefore, the height difference between the first hydrophobic layer 2 and the second hydrophobic layer 3 is 0.3mm.

[0034] Reference Figure 1 and Figure 2 The first and second hydrophobic layers 2 and 3 are both screen-printed with a hydrophobic agent selected from at least one of polytetrafluoroethylene, polyvinylidene, epoxy resin, polyphenylene sulfide, and polyimide. The screen printing process is mature and easy to operate, and the entire production process does not incur significant additional costs, making it suitable for large-scale application.

[0035] Reference Figure 1 As a preferred solution: the plate body 1 is made of high-temperature graphite or flexible graphite. Therefore, the present invention performs surface modification on the basis of the finished graphite plate to form a hydrophobic layer. The preparation process is simpler and easier to control.

[0036] Reference Figures 1 to 3 The surface modification method of the graphite plate comprises the following steps:

[0037] S1. Design a printing pattern of the screen printing plate according to the structure of the flow channel 11 of the finished graphite plate so that the mesh of the screen printing plate is aligned with the flow channel 11;

[0038] S2, applying a hydrophobic agent to the flow channel 11 by screen printing;

[0039] S3 , curing the finished graphite plate coated with the hydrophobic agent to form a hydrophobic layer in the flow channel groove 11 .

[0040] In step S1, the screen printing plate is characterized in that mesh holes are only opened at the position of the flow channel 11, and other positions are non-transparent areas. Preferably, in this embodiment, the width of the flow channel 11 is 0.5-1mm, so the aperture size of the mesh hole is designed to be 0.1mm-1mm. In application, it can also be reasonably set according to actual needs to accurately control the coating amount of the hydrophobic agent.

[0041] In step S2, in order to ensure that the hydrophobic agent in the flow channel 11 is uniform and the thickness is controllable, it is necessary to optimize the screen printing scraper pressure and scraper speed. Preferably, the screen printing scraper pressure is 5-25 kPa and the scraper speed is 1-20 cm / min.

[0042] In step S3, a curing furnace is used to cure the finished graphite plate coated with the hydrophobic agent at a curing temperature of 100-200°C.

[0043] In step S2, the hydrophobic agent in this embodiment is preferably polytetrafluoroethylene. In order to ensure the permeability of the hydrophobic agent and the molding quality of the hydrophobic layer, the viscosity of the hydrophobic agent needs to be adjusted and the viscosity is controlled at 5-30 cP. In order to reduce bubbles, a defoaming agent can also be added to the hydrophobic agent.

[0044] The hydrophobic layer of the present invention includes a first hydrophobic layer 2 and a second hydrophobic layer 3 of different heights. The first hydrophobic layer 2 and the second hydrophobic layer 3 can be prepared by printing in one step using the same screen printing plate with different mesh apertures, or by printing in two steps using two screen printing plates with different printed patterns. The following describes different screen printing methods in detail:

[0045] Reference Figure 1 、 Figure 2 and Figure 4 In the first embodiment, the first hydrophobic layer 2 and the second hydrophobic layer 3 are prepared by printing the same screen printing plate with different mesh apertures in one step. The specific preparation method includes the following steps:

[0046] Step S11: Divide the same flow channel 11 into a plurality of first coating areas and second coating areas that are alternately arranged, and design a printing pattern of the silk screen according to the structure of the flow channel 11 so that the aperture of the silk screen mesh corresponding to the first coating area is smaller than the aperture of the silk screen mesh corresponding to the second coating area;

[0047] Step S12: Applying a hydrophobic agent to the first coating area and the second coating area of ​​the flow channel 11 using a silk screen printing screen. Since the aperture of the silk screen mesh corresponding to the first coating area is smaller than the aperture of the silk screen mesh corresponding to the second coating area, the hydrophobic agent in the first coating area is less than that in the second coating area.

[0048] Step S13: placing the finished graphite plate coated with the hydrophobic agent in a curing furnace for curing treatment, so that the first hydrophobic layer 2 and the second hydrophobic layer 3 are formed in the first coating area and the second coating area respectively.

[0049] Reference Figure 1 、 Figure 2 and Figure 5 In the second embodiment, the first hydrophobic layer 2 and the second hydrophobic layer 3 are prepared by printing twice using two silk screens with different printing patterns. The specific preparation method includes the following steps:

[0050] Step S21: Divide the same flow channel 11 into a plurality of first coating areas and second coating areas that are alternately arranged, and design the printing patterns of the first and second silk screen printing plates according to the structure of the flow channel 11 so that the mesh of the first silk screen printing plate is aligned with both the first and second coating areas, while the mesh of the second silk screen printing plate is aligned only with the second coating area;

[0051] Step S22: First, a hydrophobic agent is evenly applied to the first coating area and the second coating area of ​​the flow channel 11 using a first screen printing screen, thereby completing a primary printing process; then, a hydrophobic agent is evenly applied to the second coating area using a second screen printing screen, thereby completing a secondary printing process;

[0052] Step S23 , placing the finished graphite plate coated with the hydrophobic agent in a curing furnace for curing treatment, so that a first hydrophobic layer 2 and a second hydrophobic layer 3 of different heights are formed in the first coating area and the second coating area, respectively.

[0053] The present invention uses a screen printing process to apply a hydrophobic agent to the flow channel 11 and solidify it to form a hydrophobic layer. The process is simple, easy to operate, and can be widely promoted and used. Compared with the existing technology, the preparation method provided by the present invention directly modifies the surface of the finished graphite plate. Therefore, there is no problem of impregnation or resin curing processes destroying the hydrophobic layer, making the hydrophobic layer structure of the graphite plate more reliable.

[0054] The above is only a specific implementation of the present invention, but the design concept of the present invention is not limited to this. Any non-substantial changes to the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. A method for surface modification of a graphite plate, characterized in that: The graphite plate includes a plate body and a hydrophobic layer, wherein the hydrophobic layer includes a first hydrophobic layer and a second hydrophobic layer. The surface of the plate body has a plurality of flow channels, and the plurality of first and second hydrophobic layers are spaced apart from each other in the same flow channel. The height of the second hydrophobic layer is greater than that of the first hydrophobic layer and less than that of the flow channel. The surface modification method comprises the following steps: S1. Design the printing pattern of the screen printing plate according to the flow channel structure of the finished graphite plate so that the mesh of the screen printing plate is aligned with the flow channel; S2. Applying a hydrophobic agent to the flow channel by screen printing; S3. Curing the finished graphite plate coated with the hydrophobic agent to form the first hydrophobic layer and the second hydrophobic layer in the flow channel.

2. The surface modification method of a graphite plate according to claim 1, wherein: In step S1, the same flow channel is divided into a plurality of first coating areas and second coating areas that are alternately arranged, and the aperture of the silk screen mesh corresponding to the first coating area is smaller than the aperture of the silk screen mesh corresponding to the second coating area; in step S2, a hydrophobic agent is applied to the first coating area and the second coating area of ​​the flow channel through a silk screen, so that the hydrophobic agent in the first coating area is less than the hydrophobic agent in the second coating area; in step S3, the finished graphite plate coated with the hydrophobic agent is cured, so that the first hydrophobic layer and the second hydrophobic layer are formed in the first coating area and the second coating area, respectively.

3. The surface modification method of a graphite plate according to claim 1, wherein: In step S1, the same flow channel is divided into several first coating areas and second coating areas that are alternately arranged, and a first silk screen screen and a second silk screen screen are made, with the mesh holes of the first silk screen screen aligned with the first coating area and the second coating area, and the mesh holes of the second silk screen screen aligned with the second coating area; in step S2, a hydrophobic agent is first evenly coated on the first coating area and the second coating area of ​​the flow channel through the first silk screen screen, and then the hydrophobic agent is coated on the second coating area through the second silk screen screen; in step S3, the finished graphite plate coated with the hydrophobic agent is cured so that the first hydrophobic layer and the second hydrophobic layer are formed in the first coating area and the second coating area, respectively.

4. The surface modification method of a graphite plate according to claim 1, wherein: The second hydrophobic layers in two adjacent flow channel grooves are arranged in a staggered manner.

5. The surface modification method of a graphite plate according to claim 1, wherein: The height difference between the second hydrophobic layer and the first hydrophobic layer is 0.2-0.3 mm.

6. The surface modification method of a graphite plate according to claim 1, wherein: In step S2, the screen printing scraper pressure is 5-25 kPa, and the scraper speed is 1-20 cm / min.

7. The surface modification method of a graphite plate according to claim 1, wherein: In step S3, a curing furnace is used to cure the finished graphite plate coated with the hydrophobic agent at a curing temperature of 100-200°C.

8. The surface modification method of a graphite plate according to claim 1, wherein: In step S2, the hydrophobic agent is selected from at least one of polytetrafluoroethylene, polyvinylidene, epoxy resin, polyphenylene sulfide and polyimide, and the viscosity of the hydrophobic agent is 5-30 cP.

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